General health literacy can be defined as a person's ability to obtain, process, and understand the basic health information needed to make appropriate health care decisions. The Institute of Medicine has put forth a model of health literacy that includes four constructs: 1) cultural and conceptual knowledge, 2) oral literacy (listening and speaking), 3) print literacy (writing and reading) and 4) numeracy. Each construct reflects a set of skills required to function in the health care system and each requires a valid measure to move forward our understanding of the relationship between literacy and health. We propose to develop a new measure of health literacy based upon a conceptual framework of the health numeracy construct. We have developed a conceptual framework of health numeracy that includes the domains of primary numeric skills, applied health numeracy, and interpretive health numeracy. A comprehensive and valid numeracy measure will advance the science of communication and decision-making by: a) providing a tool to describe the level and components of numeracy present in a given individual or population, b) guiding the development of tailored communication and patient educational materials, and c) supporting the development of interventions to improve health numeracy skills. The specific aims in this application are: 1. To develop a measure of health numeracy named the Numeracy Understanding in Medicine Instrument (NUMi). The NUMi will be a. Based upon an empirically derived framework of health numeracy. b. Cross-culturally equivalent across race (black and white) and ethnic (Hispanic and Non-Hispanic) groups. c. Developed using Item Response Theory to ensure that the estimated characteristics of the items are invariant with respect to the sample that is used to evaluate the measure. 2. To establish the reliability and validity of the NUMi a. Internal reliability and parallel-testing reliability will be conducted. b. Content validity will be supported by expert panel review of the numeracy construct, review of the skills identified to reflect the numeracy construct, and review of the items generated for the NUMi instrument. c. Construct validity will tested by evaluating the association of scores on the NUMi with levels of education and existing measures of achievement and health literacy. d. Criterion validity will be tested by evaluating the association of scores on the NUMi with the Medical Data Interpretation Test, the adoption of health protective behaviors, and perceived health.